During the quation analysis of a mixture containing `Cu^(2+) and Zn^(2+) ions H_(2)S` gas is passed therough an acidified solution containing these ions in order to test `Cu^(2+)` alone explane

Explanation

`H_(2)S hArr 2H^(o+) +S^(2-)`
`HCI rarr H +CI^(Theta)`
`K_(sp) `(solubility product) of `CuS` is less than `K_(sp)` of `ZnS `.Due to common ion effect ,the ionisation of `H_(2)S` is sappressed and the `S^(2-)` concentration decreases
Only those metal sulphides get precipitate which have low `K_(sp)` so ZnS is not precipitate.